In this courtroom sketch, Gilberto Valle is seen in federal court in New York on Monday.

NEW YORK — A New York City police officer’s bizarre Internet discussion of cannibalism — what he claims was harmless fantasy — was instead a serious plot to abduct, torture and eat “very real women,” a federal prosecutor said Monday at the officer’s kidnapping conspiracy trial.

“Make no mistake,” Assistant U.S. Attorney Randall Jackson told a jury. “Gilberto Valle was very serious about these plans.”

But defense attorney Julia Gatto argued that her client “never intended to kidnap anyone.” She added: “You can’t convict people for their thoughts, even if they’re sick.”

The exchange came during opening statements in one of the strangest cases in Manhattan federal court in recent memory.

Valle, 28, is charged with conspiring to kidnap a woman and unauthorized use of a law enforcement database, which prosecutors say he used to help build a list of potential targets. A conviction on the kidnapping count carries a possible life sentence.

A college graduate and father of a young child, Valle appeared to be leading a normal life before he began acting “extremely strangely,” Jackson said.

It became clear to Valle’s wife that something was wrong, so she put a program on his computer to trace where he went online, Jackson said. Online discussions revealed his plans to “sexually assault these women ... to slit their throats and detailed plans to cannibalize these women,” he said.

Once his wife reported his strange behavior to the FBI last year, agents uncovered “a heinous plot to kidnap, rape, murder and cannibalize a number of very real women,” the prosecutor said.

Claims by lawyers for Valle that he was only indulging in fetish fantasies are “utterly bogus,” Jackson added.

The officer had attempted to contact potential victims, including a New York City elementary school teacher, to learn more about their jobs and residences, the prosecutor said. His Internet research also included the best rope to tie someone up with, recipes, human flesh, white slavery and chemicals that can knock someone out, Jackson said.

Gatto argued that there was “no proof of a crime here. The charges are pure fiction.”

Valle, she said, had always been aroused by “unusual things” including the thought of a woman boiled down on a platter with an apple in her mouth, his lawyer said. He found a home at darkfetishnet.com with its 38,000 registered members, where they regularly discuss “suffocating women, cooking and eating them,” she said.

The government was expected to call Valle’s wife, Kathleen Mangan, as its first witness.

Before opening statements, U.S. District Judge Paul G. Gardephe set strict parameters for Mangan’s testimony, saying she can tell a jury about discovering her husband’s morbid discussions but not about the couple’s confidential communications or about his mental condition.

Prosecutors said in court papers that Mangan fled their home on Sept. 10, 2012, believing he was planning to kidnap, rape, torture and murder her. She also discovered that he “had similarly heinous plans for women she knew and to whom she was close,” prosecutors wrote.

The defense has denied that Mangan was a potential victim. Valle had made clear that his wife “was unavailable for any kidnapping fantasy,” the defense papers said.

Valle, a baby-faced tabloid sensation known as the “Cannibal Cop,” is expected to take the stand to make the case that it was all role-playing fantasy played out on Internet sites like darkfetishnet.com.

The defense also is planning to show jurors the videotaped testimony of darkfetishnet.com co-founder Sergey Merenkov in which he describes the site as a “social media network.”

Merenkov called the site “a clone of Facebook, but it is oriented to people with fetishes that are not considered standard.”

Asked the most popular fetishes, Merenkov responds, “All sorts of asphxiation” and “peril cannibalism.”

Tiger Howard Devore, a psychologist and certified sex therapist who specializes in dealing with sexual dysfunction and fetishes, said the cannibalism fetish known as voreaphilia isn’t common.

“For most laymen, they’re going to think about it as cannibalism,” Devore told The Associated Press on Monday. “But what it really is, is an obsession about consuming the flesh of the other, and this can have a whole range of expressions. ... It is mostly played out in fantasy, mostly played out in role-playing.”

There are well-known criminal extremes like Jeffrey Dahmer, who saved pieces of his victims’ body parts and ate the flesh, Devore said, though “the instances of this kind of violence are extremely rare.”